New deck time to stain?

My cedar deck was built last November. I was told but just checking for more opinions and info. That I should oil stain late this summer wood should be dry enough. But we had such a dry mild winter wondering if I could do it sooner?

Also:
If it does rain how long should I wait with dry days before staining?
Do all surfaces need to be stained? Underside and posts as well? Use a roller for that for minimal drip waist?
Any other advice on staining a new deck?

Thanks!